Differential neutralizing capacity to different human immunodeficiency virus (HIV) isolates by a rabbit antiserum against LAV: sensitive assays with HTLV-I-positive MT-4 cells.

A rabbit antiserum against LAV was prepared. This serum reacted with both LAV and HTLV-III identically in the immunodiffusion and immunoprecipitation. It was also confirmed that the rabbit serum in the immunofluorescence (IF) studies contained several isolates of human immunodeficiency virus (HIV) including LAV, HTLV-III, ARV and YU-6 similarly as human reference antibodies. The neutralizing capacity of this antiserum to HTLV-III and YU-6 isolates was further studied using three methods, such as 3[H]-thymidine uptake in HIV infected MT-4 cells, IF assay, and plaque forming assay. All experiments showed that the rabbit antiserum could not neutralize YU-6 but HTLV-III, while human sera neutralized both viruses equally. These data suggest that rabbit antibody recognizes narrower neutralizing epitopes than HIV-infected human antibodies, although there exist no differences as to recognition of antigens responsible for IF between them. Furthermore, we showed that this type-specific neutralization was not due to the absorption of neutralizing serum by the noninfectious viral particles. These data may be important in understanding heterogeneities of HIV and in development of an effective vaccine.